Why your duct leaks matter more than your thermostat setting

Most homes we test are losing somewhere between a fifth and a third of their conditioned air through duct leaks before it ever reaches a room — attic joints, crushed flex duct, and connections that were taped rather than mastic-sealed during the original build.

That means the system is working to cool or heat air that is escaping into an unconditioned attic, then working again to replace it. No thermostat setting fixes that; it just makes the system run longer to compensate, which is the part that actually shows up on the power bill.

A duct test and seal is a smaller, less dramatic fix than a new system, which is probably why it gets skipped. It is also usually the highest-value thing we can do on an older system that is technically working fine but costing more to run than it should.